Inclusion Criteria:

• Male or female subjects aged 18 years or older
• Histologically confirmed primary DLBCL of any stage
• Refractory to the last treatment regimen
• Previously treated with the following treatment regimens:
• Anthracycline-based combination chemotherapy with rituximab
• Second-line combination chemotherapy
• Autologous BMT if the subject was eligible and did not refuse the procedure
• At least one measurable lesion defined as > 1.5 cm in the longest diameter
• No known central nervous system involvement
• ECOG performance status < 2
• Life expectancy > 12 weeks
• If female, non-pregnant and non-lactating
• IRB-approved consent and HIPAA Authorization

Exclusion Criteria:

• Transformed, composite or discordant lymphoma
• Therapy for lymphoma within 21 days prior to the first dose of YM155
• Within 4 weeks of the screening FDG-PET scan, receipt of the following:
• Radiation therapy
• Surgical procedures (except biopsies and central catheter / port placement)
• Active infection (bloodstream or deep tissue)
• Inadequate marrow, hepatic and/or renal function
• Serum creatinine > 1.5 x ULN or calculated serum creatinine clearance < 60 mL/min
• Absolute Neutrophil Count (ANC) < 750/mm3
• Platelet < 50,000/mm3
• Alanine Transaminase (ALT) and Aspartate Transaminase (AST) > 2.5 x ULN; > 5 x ULN if secondary to liver metastases
• Treated with > 3 prior treatment regimens. The following should be considered:
• Planned maintenance therapy should be considered as part of the previous treatment regimen
• Any preparative treatment (salvage chemotherapy, high-dose chemotherapy, radiation therapy, etc.) should be included with the autologous BMT or PBSCT as one treatment
• Prior allogeneic BMT or PBSCT
• Previously treated with YM155
• Other investigational therapy or procedures within 28 days
• Known HIV, hepatitis B surface antigen, or hepatitis C antibody
• Other malignancy requiring treatment within 2 years
• Significant and/or uncontrolled cardiac, renal, hepatic, or other systemic disorders or significant psychological conditions that in the Investigator's judgment would jeopardize subject enrollment or compliance